Web materials, such as thermoplastic films, have a variety of uses including component materials of absorbent articles (such as topsheets and backsheets), packaging (such as flow wrap, shrink wrap, and polybags), trash bags, food wrap, dental floss, wipes, electronic components, and the like. For many of these uses of web materials, it can be beneficial for the web material to have a textured surface which can provide the surface of the web material with a desirable feel, visual impression, and/or audible impression.
Polymeric webs exhibiting a soft and silky tactile impression can be made via a vacuum forming process or a hydroforming process. With a typical vacuum forming process, a precursor web is heated and placed over a forming structure. Then a vacuum forces the precursor web to conform to the texture of the forming structure. The resulting polymeric web has texture that can provide a soft and silky tactile impression, depending upon the texture of the forming structure and degree of conformation. While a vacuum forming process can be suitable for making a soft and silky polymeric web, a vacuum forming process is typically limited with respect to the amount of pressure capable of being exerted onto a precursor web. As a result, it is usually required to heat a precursor film to significantly soften or melt the precursor film prior to placement on the forming structure in order to vacuum form the precursor film to the forming structure. A vacuum forming process is therefore an inefficient process in terms of how fast the process can be performed due to the heating step and the limited pressures generated by the process.
With a typical hydroforming process, a precursor web is placed over a forming structure and high pressure and high temperature water jets force the precursor web to conform to the texture of the forming structure. The resulting polymeric web can have texture that can provide a soft and silky tactile impression, depending upon the texture of the forming structure. A hydroforming process, although capable of producing soft and silky polymeric webs, is typically a costly and inefficient process involving the use of high pressure and high temperature water jets and subsequent drying steps, including dewatering steps.
Embossing is a process that typically involves the act of mechanically working a substrate to cause the substrate to conform under pressure to the depths and contours of a pattern engraved or otherwise formed on an embossing roll. It is widely used in the production of consumer goods. Manufacturers use the embossing process to impart a texture or relief pattern into products made of textiles, paper, synthetic materials, plastic materials, metals, and wood.
Embossing processes have been used to provide texture to polymeric films. However, such embossing processes typically require extruding a molten resin onto a forming structure or heating a precursor web before placement onto a forming structure and then embossing to produce an embossed web. The embossed web is then cooled, typically by cooling the embossing rolls or plates used to emboss the heated precursor web or molten resin. The cooling step is often utilized to set the texture in the embossed web. However, these heating and cooling steps add undesirable cost and inefficiency, as well as complexity, to the process. In addition, such embossing processes typically involve relatively large dwell times, which can result in slow, inefficient processes.
It is also typically difficult to impart relatively small scale texture to precursor webs using conventional embossing processes. Furthermore, typical embossing processes tend to produce embossed webs having relatively uniform thickness throughout the web.
For example, U.S. Pat. No. 5,972,280 discloses an embossing process utilizing a hot engraved surface of an embossing roll and static pressure applied within a chamber to heat a web and deform it over the surface of the embossed roll. This process uses elevated temperatures, which are typically above the softening temperature of the web, and relatively low pressures of about 0.007 MPa to about 0.7 MPa. As a result, the embossed pattern is formed as indentations disposed on only a single surface of the web, without affecting the opposite surface of the web.
Despite the knowledge in the art, there remains a desire to develop a more efficient process for making embossed webs that have desirable feel, visual impression, and/or audible impression, especially embossed webs exhibiting thinning in desirable areas of the embossed web. In certain aspects, a desired process is efficient with respect to the energy and resources required by the process. In certain aspects, a desired process is capable of running at high speeds. In certain aspects, a desired process is capable of running at relatively low temperatures, such as ambient temperature.